Action: There was a communication error that requires further investigation. First, check for network problems and review the SQL*Net setup. Also, look in the alert.log file for any errors. Finally, test to see whether the server process is dead and whether a trace file was generated at failure time.

Also, have a look at My Oracle Support.]]>Littlefoot2012-12-30T15:30:51-00:00Re: Oracle 11g Idle instancehttp://www.orafaq.com/forum/./mv/msg/185519/573530/#msg_573530
Have a look at alert.log and trace files.
You can also read this article: Troubleshooting Internal Errors.